GABA agonists and omega conotoxin GVIA modulate responses to nerve activation of the perfused rat mesentery

Abstract

The modulatory actions of γ-aminobutyric acid (GABA) receptor agonists and ω-conotoxin GVIA (CTX) on sympathetic and sensory nerves were examined on contractile responses of the perfused rat mesentery to transmural nerve stimulation (TNS). GABA and baclofen, a selective GABA B receptor agonist, significantly inhibited vasoconstrictor responses to TNS, while muscimol, a selective GABA A receptor agonist, had no effect. In the guanethidine treated and methoxamine-contracted mesentery, TNS caused a vasodilator response which was unaffected by GABA. CTX (10 −8 M) markedly suppressed the vasoconstrictor response to TNS, but did not affect vasodilator responses. These findings suggest that in the rat mesentery: (1) GABA receptors modulate the activity of sympathetic nerves via prejunctional GABA B receptors, but do not influence sensory nerves, and (2) calcium channels which participate in sympathetic nerve activation have different properties than calcium channels in capsaicin-sensitive sensory nerves.